Dielectric study of Rb0.75(ND4)0.25D2AsO4

The complex dielectric constant of Rb 0.75 (ND 4 ) 0.25 D 2 AsO 4 along the tetragonal crystallographic c axis has been measured as a function of temperature for frequencies between 100 Hz and 1 MHz. The dielectric relaxation is described using a Frohlich-type distribution function. The expressions for epsilon ' and epsilon " are evaluated on this basis and fitted to the experimental data. The characteristic central frequency f epsilon obeys an Arrhenius law and the relaxation process is polydispersive. Below the freezing temperature T f =68.9 K the dielectric intensity epsilon (0)- epsilon ( infinity ) is decreasing with decreasing temperature and its temperature dependence can be described by the replica-symmetry-breaking solution of the infinite range Ising spin glass model in the presence of random fields.